Semiconductor lasers are currently used in a variety of technologies and applications, including communications networks. One type of semiconductor laser is the distributed feedback (“DFB”) laser. The DFB laser produces a stream of coherent, monochromatic light by stimulating photon emission from a solid state material. DFB lasers are commonly used in optical transmitters, which are responsible for modulating electrical signals into optical signals for transmission via an optical communication network.
Generally, a DFB laser includes a positively or negatively doped bottom layer or substrate, and a top layer that is oppositely doped with respect to the bottom layer. An active region, bounded by confinement regions, is included at the junction of the two layers. These structures together form the laser body. A coherent stream of light that is produced in the active region of the DFB laser can be emitted through either longitudinal end, or facet, of the laser body. One facet is typically coated with a high reflective material that redirects photons produced in the active region toward the other facet in order to maximize the emission of coherent light from that facet end. A grating is included in either the top or bottom layer to assist in producing a coherent photon beam. DFB lasers are typically known as single mode devices as they produce light signals at one of several distinct wavelengths, such as 1,310 nm or 1,550 nm. Such light signals are appropriate for use in transmitting information over great distances via an optical communications network.
In traditional DFB lasers and other high-speed ridge waveguide lasers, there is often excessive lateral current spreading in various layers between the bottom of the ridge and the active region that results in reduced injection of carriers into the action region. This reduces both the gain and differential gain, which in turn can negatively affect both the DC and RF performance characteristics of the laser.